Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2001-08-08
2003-09-09
VerSteeg, Steven H. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298040, C204S298110, C204S298230, C204S298270, C204S298280, C118S712000, C118S715000, C118S720000, C118S7230AN, C118S504000
Reexamination Certificate
active
06616818
ABSTRACT:
This invention relates to an apparatus and a method for coating substrates. The apparatus and method may also be applicable to cleaning substrates. More particularly, the invention relates to an apparatus and a method for the vacuum deposition of a vaporised coating material on a substrate.
The thickness uniformity of evaporated films to high precision levels over extended areas is becoming a key requirement in a range of applications.
This is particularly the case for multilayer dielectric optical coatings for precision applications such as dense wavelength division multiplexer (DWDM) filters, which demand ±0.02% thickness control. Production demands for such filters are driving the need to extend such thickness control over increased areas thereby maximising production throughput. The reasons for the limitations in achieving thickness uniformity are complex, but lie mainly in stability and control of the spatial distribution of the evaporation plume from the deposition source, particularly over extended deposition times. Mechanical masking techniques, static (H. Anders, Dr. H. Anders Company, D-8470, Nabburg, Germany; H. Donz, Thesis, Inst. Of Experimental Physics, University of Innsbruck, Austria; Th. Kraus, Vakuum Techn., 31 (1982), 130) and dynamic (L. G. Schultz, J. Opt. Soc. Am., 38 (1948) 432) are well demonstrated to achieve film thickness uniformity, but these rely upon stable spatial distribution in the evaporant plume.
The increase in substrate to evaporant surface distance as material is consumed within the source material is an important source of variation in spatial distribution of the evaporant plume. Another detrimental consequence of this effect is a change in evaporating species characteristics at the source material—for example, when using electron beam vaporisation there may be a change in the electron beam spot diameter with increased distance beam travels due to source depletion.
It has been described in “G. Deppisch, Vakuum-Techn., 30 (1981) 67”, that for a point evaporation source, this effect causes film thickness non-uniformity to increase as a consequence of reducing relative thickness at the edge compared with centre of the coated area.
For a 2% change in source material to substrate distance (typical for ultra-high precision applications such as DWDM), the effective change in uniformity is of the order of 0.05% over typical substrate areas (4 inch to 8 inch (10.2 to 20.4 cm) diameter). This level of non-uniformity significantly reduces the useable area of the substrate. The present invention makes it possible to reduce or even eliminate the effects of this problem.
We have now found a way of improving the uniformity of thickness of the deposited layers beyond what is possible using static or dynamic masking.
In accordance with one broad aspect of the invention, the distance between the source material and the substrate is adjustable. This makes it possible to move the source material to take account of the increased distance between the surface of the source material and the substrate which take place as the source material is depleted.
In accordance with another broad aspect of the invention, a beam used to vaporise the source material may have its frequency or diameter adjusted to take account of the variations in the surface of the source material which take place as the source material is depleted. This makes it possible to reduce or even eliminate the effects of the change in the profile of the source material surface as a consequence of the evaporation process. This is another source of variation in spatial distribution of the evaporant plume. Surface profile changes introduces a greater range of presented surface angles to the evaporating species (i.e. electron beam or ion flux for sputter deposition).
The present invention also provides a means of monitoring the spatial distribution of the evaporant plume and utilising such information to control substrate to evaporant surface distance, and, for electron beam deposition, to modify electron beam scan. Significant improvements in film thickness uniformity have been achieved.
According to one aspect of the invention there is provided an apparatus for treating a substrate, comprising: a vacuum chamber; a substrate carrier adapted to carry a substrate to be treated; a source material holder for holding a source material with which the substrate is to be treated; and vaporising/sputtering means for vaporising/sputtering the source material; wherein the source material holder includes a positioning means for relatively moving the source material towards the substrate carrier.
Thus, the apparatus according the invention makes it possible to adjust the distance between the substrate and the surface of the source material (i.e. the material to be vaporised for subsequent deposition on the substrate). The distance could be adjusted by movement of the source material holder, by movement of the substrate carrier, or both. It is preferred that it is only the source material holder that is moved. The adjustment of the distance can maintain a substantially constant distance between the surface of the source material and the substrate carrier, or, preferably, the surface of the source material and the surface of the substrate being treated. Where the treatment involves deposition of the source material, the thickness of the substrate increases while the thickness of the source material decreases—the present invention is capable of dealing with this phenomenon.
Typically the treatment comprises either coating or cleaning the substrate. From this point on the invention will be described in relation to the coating of substrates, but it will be appreciated that the features of the invention described hereinbelow are equally applicable to the cleaning of substrates.
Furthermore the apparatus is equally applicable to coating techniques involving vaporising or sputtering. Vaporising techniques involve the use of a means to heat and vaporise (i.e. evaporate) the source material. These techniques commonly use (1) an electron beam vaporiser, in which the source material is vaporised by means of a vaporising beam in the form of a stream of electrons; or (2) a thermal vaporiser, in which the source material is vaporised by the application of heat. Sputtering techniques involve the bombardment of the source (which is usually called a target) with a broad plasma (known as “sputtering”) or with an ion beam (known an “ion beam sputtering”). In sputtering techniques the target is usually electrically biased to attract ions from the plasma or ion beam. From this point on the invention will be described in relation to the vaporisation techniques, but it will be appreciated that the features of the invention described hereinbelow are equally applicable to sputtering techniques.
It is especially preferred that the positioning means can move the source material linearly, so that the source material can be moved linearly towards the substrate. In most embodiments, the linear movement will take place in a substantially vertical direction. It is also preferred that the positioning means can move the source material away from the substrate carrier as well as towards it.
Preferably, the source material holder further comprises a receptacle adapted to contain the source material, this receptacle being known in the art as a hearth. The positioning means acts on the receptacle to move it in the desired direction.
It is possible for the positioning means to be arranged to move both the receptacle and the vaporising means relative to the substrate carrier, so that there is no relative movement between the source material holder and the vaporising means (other than a possible relative rotation of the receptacle as described below). However, in an especially advantageous embodiment, the positioning means is capable of moving the source material linearly relative to the vaporising means. This makes it possible for the surface of the source material to be adjusted relative to a vaporising beam generated by the vaporising means.
In t
Hobbes Laurence P.
Roberts Peter W.
Roberts Mlotkowski & Hobbes PC
RTC Systems Ltd.
VerSteeg Steven H.
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